[CM] something like let-set! for undefined vars?

[Iain Duncan]

Hi folks, I've been digging into S7s environment support and loving it. I
have implemented a really convenient pseudo-inheritance-through-delegation
setup for my process objects, and one thing I'm using is the let-set!
function to allow updating internal variables from outside if desired. My
little method looks like this (in side of a let inside a function)

(define (set sym val)
      ;; TODO this doesn't allow setting values that are not yet set
      ;; need to check if symbol is in let and then set it
      (let-set! proc-env sym val))

However, this of course errors if I try to use if and sym is not defined. I
tried mucking about with the defined?  predicate, but got confused by the
docs. If anyone can tell me how I can easily add to the above the
following, that would be lovely:

- if sym not defined in proc-env, define sym to val

iain
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://cm-mail.stanford.edu/pipermail/cmdist/attachments/20210206/6d3c6452/attachment.html>